The present disclosure relates to a sheet transport device that feeds a sheet in a predetermined direction, and an image forming apparatus including same, such as a copying machine, a printer, a fax machine, or a multifunctional peripheral having functions of them. The present disclosure also relates to a sheet transport device that feeds a sheet in a predetermined direction in a confluence transport path where a plurality of sheet transport paths merge, and an image forming apparatus including same.
An image forming apparatus is provided with a sheet transport device that feeds sheets in a paper cassette to a transfer section one at a time, feeds a sheet to which a toner image is transferred to a fixing section, and then feeds the sheet to an ejection section. This sheet transport device has a plurality of transport roller pairs. Due to the rotation of the transport roller pairs, a sheet is fed along a transport path. In such a sheet transport device, a sheet is fed to the transfer section at a predetermined timing, and the direction of the sheet to which an image is transferred is appropriately maintained. For example, the leading edge of the sheet comes into contact with the nip section of the registration roller pair and stops. Even after the leading edge of the sheet stops, the rear part of the sheet is fed. Thus, the sheet is curved. At this time, the rear part of the sheet is restrained by a transport roller pair. Therefore, if the leading edge of the sheet is skewed relative to the nip section, the leading edge of the sheet is aligned with the nip section of the registration roller pair, and the skew of the sheet is corrected.
Examples of such a sheet transport device that corrects the skew include a sheet transport device in which a sheet transport path on the upstream side of the registration roller pair is curved and that has a stationary guide member provided on the concave side of the curved sheet transport path. A movable guide member is provided on the convex side of the sheet transport path so as to face the stationary guide member and rotatably supported in the vicinity of the upstream end. A film-like member is provided that protrudes from the front edge of the movable guide member to the downstream side in the sheet transport direction. A spring urges the movable guide member toward the stationary guide member. In this sheet transport device, a sheet whose leading edge has reached the registration roller pair curves along the sheet transport path. At this time, the sheet is deflected toward the movable guide member, and the movable guide member is pressed by the convex side of the curved sheet, but the convex side of the sheet is held down by the spring. Therefore, the leading edge of the sheet is pressed against the nip section of the registration roller pair, and the skew of the sheet is corrected.
However, in the above sheet transport device, the contact of the sheet with the movable guide member increases the transport load. Therefore, it is necessary to use a high-performance motor, and this may increase the cost.
In another exemplary sheet transport device, a movable guide capable of being bent like a loop is provided on the upstream side of the registration roller pair. When the leading edge of the sheet comes into contact with the nip section of the registration roller pair, the sheet bends like a loop. The skew of the sheet is thereby corrected. The movable guide is pressed along the deflection of the sheet and is deformed like a loop. The sheet comes into contact with the movable guide before the movable guide forms a loop. This configuration may reduce the transport noise generated between the sheet and the movable guide.
Still another exemplary sheet transport device uses a plurality of sheet transport paths, and reduces the transport noise generated when a sheet transported from each sheet transport path comes into contact with the registration roller pair and undergoes deflection. In this sheet transport device, a guide member is provided in the sheet transport direction of each sheet transport path, and two elastic films are positioned so as to be in contact with the guide member. When a sheet comes into contact with the registration roller pair and undergoes deflection, the most bulging part of the sheet comes into contact with the area around the contact point of the two elastic films. Therefore, the sheet is not bent rapidly, and the vibration of the sheet is suppressed. This configuration reduces the transport noise.